Women have a tendency to see other women as their competition. This is 100% rubbish. There is only one unique you in this world. Your competition is the best version of yourself. So be that best version and eliminate the competition.
If a guy isn’t interested in you, it’s not because of another woman – it’s because for whatever reason, you aren’t what he’s looking for. This isn’t necessarily a bad thing – maybe he knows something about himself that would make you two a bad match.
If you encounter a guy who is trying to put you into competition with another female then you should walk away immediately and don’t look back. He isn’t interested in you, he just wants to watch the catfight. (Shame on him – I bet his momma is ashamed.)
Other women are your support system but they need to be cultivated as such. Of course there will always be “mean girls” who aren’t quite as secure as they appear and feel the need to attack other women – ignore them, you don’t need the hassle. Concentrate on building worthwhile friendships with women – you need a best friend and it shouldn’t be your significant other.